AQA A-Level Chemistry 7405/2 Paper 2 Exam Actual
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SECTION 1: PHYSICAL CHEMISTRY (14 Questions)
Q1: For the reaction A + B → C, the rate equation is determined to be rate = k[A]²[B].
What is the overall order of the reaction?
A. First order
B. Second order
C. Third order [CORRECT]
D. Zero order
Correct Answer: C
Rationale: Correct because the overall order is the sum of the individual orders with
respect to each reactant; 2 + 1 = 3, making this a third-order reaction overall.
Q2: Which change to a system at equilibrium will increase the value of the
equilibrium constant Kp?
A. Increasing the concentration of a reactant
B. Increasing the pressure
C. Changing the temperature [CORRECT]
D. Adding a catalyst
,Correct Answer: C
Rationale: Correct because the equilibrium constant Kp is temperature-dependent
only; changing concentration, pressure, or adding a catalyst shifts the equilibrium
position but does not alter the value of Kp.
Q3: The standard enthalpy change of formation (ΔHf°) of an element in its standard
state is:
A. The enthalpy change when one mole of the element is formed from its constituent
atoms
B. The enthalpy change when one mole of the element is burned in oxygen
C. Zero by definition [CORRECT]
D. Always positive
Correct Answer: C
Rationale: Correct because by definition, the standard enthalpy of formation of an
element in its most stable standard state (e.g., O₂(g), C(graphite)) is zero, as no
chemical change occurs when forming the element from itself.
Q4: A buffer solution is prepared containing 0.10 mol dm⁻³ ethanoic acid and 0.15
mol dm⁻³ sodium ethanoate. Which equation correctly shows the action of this
buffer when a small amount of alkali is added?
A. CH₃COO⁻ + H⁺ → CH₃COOH
B. CH₃COOH + OH⁻ → CH₃COO⁻ + H₂O [CORRECT]
C. CH₃COO⁻ + OH⁻ → CH₃COOH + O²⁻
D. Na⁺ + OH⁻ → NaOH
, Correct Answer: B
Rationale: Correct because the weak acid component (CH₃COOH) of the buffer
neutralises added alkali (OH⁻), converting it to the conjugate base (CH₃COO⁻) and
water, thereby resisting pH change.
Q5: For a first-order reaction, a plot of which pair of variables gives a straight line?
A. Concentration vs. time
B. Rate vs. concentration
C. ln[concentration] vs. time [CORRECT]
D. 1/concentration vs. time
Correct Answer: C
Rationale: Correct because the integrated rate law for a first-order reaction is ln[A] =
ln[A]₀ − kt; a plot of ln[concentration] against time yields a straight line with gradient
−k and y-intercept ln[A]₀.
Q6: In an electrochemical cell, the salt bridge serves to:
A. Allow electrons to flow between the half-cells
B. Maintain electrical neutrality by allowing ion migration between half-cells
[CORRECT]
C. Increase the voltage of the cell
D. Prevent any reaction from occurring
Correct Answer: B
2025 with Detailed Rationales | Complete Exam-Style
Questions | Pass Guaranteed – A+ Graded
SECTION 1: PHYSICAL CHEMISTRY (14 Questions)
Q1: For the reaction A + B → C, the rate equation is determined to be rate = k[A]²[B].
What is the overall order of the reaction?
A. First order
B. Second order
C. Third order [CORRECT]
D. Zero order
Correct Answer: C
Rationale: Correct because the overall order is the sum of the individual orders with
respect to each reactant; 2 + 1 = 3, making this a third-order reaction overall.
Q2: Which change to a system at equilibrium will increase the value of the
equilibrium constant Kp?
A. Increasing the concentration of a reactant
B. Increasing the pressure
C. Changing the temperature [CORRECT]
D. Adding a catalyst
,Correct Answer: C
Rationale: Correct because the equilibrium constant Kp is temperature-dependent
only; changing concentration, pressure, or adding a catalyst shifts the equilibrium
position but does not alter the value of Kp.
Q3: The standard enthalpy change of formation (ΔHf°) of an element in its standard
state is:
A. The enthalpy change when one mole of the element is formed from its constituent
atoms
B. The enthalpy change when one mole of the element is burned in oxygen
C. Zero by definition [CORRECT]
D. Always positive
Correct Answer: C
Rationale: Correct because by definition, the standard enthalpy of formation of an
element in its most stable standard state (e.g., O₂(g), C(graphite)) is zero, as no
chemical change occurs when forming the element from itself.
Q4: A buffer solution is prepared containing 0.10 mol dm⁻³ ethanoic acid and 0.15
mol dm⁻³ sodium ethanoate. Which equation correctly shows the action of this
buffer when a small amount of alkali is added?
A. CH₃COO⁻ + H⁺ → CH₃COOH
B. CH₃COOH + OH⁻ → CH₃COO⁻ + H₂O [CORRECT]
C. CH₃COO⁻ + OH⁻ → CH₃COOH + O²⁻
D. Na⁺ + OH⁻ → NaOH
, Correct Answer: B
Rationale: Correct because the weak acid component (CH₃COOH) of the buffer
neutralises added alkali (OH⁻), converting it to the conjugate base (CH₃COO⁻) and
water, thereby resisting pH change.
Q5: For a first-order reaction, a plot of which pair of variables gives a straight line?
A. Concentration vs. time
B. Rate vs. concentration
C. ln[concentration] vs. time [CORRECT]
D. 1/concentration vs. time
Correct Answer: C
Rationale: Correct because the integrated rate law for a first-order reaction is ln[A] =
ln[A]₀ − kt; a plot of ln[concentration] against time yields a straight line with gradient
−k and y-intercept ln[A]₀.
Q6: In an electrochemical cell, the salt bridge serves to:
A. Allow electrons to flow between the half-cells
B. Maintain electrical neutrality by allowing ion migration between half-cells
[CORRECT]
C. Increase the voltage of the cell
D. Prevent any reaction from occurring
Correct Answer: B
